A vehicle may include a DC (direct current) battery configured to supply a DC voltage and a DC to AC (alternating current) inverter configured to invert the DC voltage from the battery into an AC output voltage. The AC output voltage may be used to power electrical appliances (i.e., loads) within the vehicle such as laptops and cell phones, DVD players and game station consoles, televisions, etc., which require an AC supply voltage for their operation. For example, the battery supplies a 12V DC voltage which the inverter inverts into an AC output voltage appropriate for the load (e.g., 120V RMS at 60 Hz).
The vehicle may have start/stop functionality. A problem is that when the vehicle is auto-started, which is allowed to occur while the start/stop functionality is enabled, the DC voltage supplied by the battery can dip down. For instance, the battery supplied DC voltage can dip from 12V down to 6V-8V. In turn, the inverter rating decreases such as down to 11V. Thus, when the vehicle is auto-started, the inverter output can drop out as a result of the inverter rating decreasing in response to the battery supplied DC voltage dipping. Understandably, this can cause user annoyance as the laptop and cell phone screens may flicker and their speakers may beep, the DVD player and game station console may restart, and the television may drop out and require manual operation to restart.
Accordingly, it is desirable that the vehicle is not auto-started while a load is being supplied with electrical power from the inverter (i.e., while a load is electrically connected (or “connected”) to the inverter). That is, it is desirable that the start/stop functionality be disabled while a load is being supplied with electrical power from the inverter. This is because the vehicle is not allowed to auto-start while the start/stop functionality is disabled.
In some implementations, the inverter is part of an assembly having a load sensor configured to sense the electrical current of the load (i.e., the load current). Such current sensing is used for protection (i.e., overcurrent). On the other hand, a load consuming power such as below 10% of the power ratio of the inverter is not detected by the load sensor as the corresponding current is relatively very low. Thus, the condition may occur in which a light power load connected to the inverter is not detected and it is therefore presumed that no load is connected to the inverter. Consequently, as it is presumed that no load is connected to the inverter, the start/stop functionality is not disabled and the vehicle is therefore allowed to be auto-started. As described, the operation of the load, which is in fact connected to the inverter, is compromised when the vehicle is auto-started.
In sum, the inability of detecting a light power load connected to the inverter prevents the assembly from requesting the start/stop functionality from being disabled. On the other hand, when a heavier power load is connected to the inverter the corresponding heavier current is detectable by the load sensor of the assembly. In this case, the assembly is aware of the presence of the heavier power load connected to the inverter and based on this awareness can request the start/stop functionality to be disabled.
In one configuration in which the inverter is part of an assembly having a load sensor configured to sense load current, the load sensor includes an amplifier and an analog-to-digital converter (ADC). The amplifier amplifies a voltage corresponding to the load current (for instance, the voltage tapped across a resistor in series with the load) and the ADC converts the corresponding amplified voltage to a digital output corresponding to the load current. For example, the amplifier has a gain of ten and the resistor is a 50 mOhm resistor; the full ADC sensing range is 0 A to 10 A; the overcurrent sensing range is up to 20 A (utilizing comparator and resistor divider for scaling signal down); and the 20 A range is required for over-current protection. In this exemplary configuration, with this range standard a cell phone load consuming about 4 W of power would produce only 17 mV or 3 counts on the ADC input. As such, this cell phone load would not be detected. As a result, the start/stop functionality would not be disabled even though a load (i.e., the cell phone load) is being supplied with electrical power by the inverter. Consequently, the vehicle is allowed to auto-start which would cause the operation of the cell phone load to be disrupted.
One solution to the problem caused by the battery supplied DC voltage dipping down when the vehicle is auto-started is to operate the inverter down to 6V. However, this presents significant concerns as explained as follows. First, inverter operation at 11V providing 350 W of power and operating at 90% efficiency consumes about 35 A of current, which is seen as a limit for typical vehicle wiring applications. Inverter operation at 6V providing 350 W of power and operating at 90% efficiency consumes 65 A of current and inverter operation at 6V providing a peak requirement of 800 W of power and operating at 85% efficiency consumes 156 A of current, which are both far over the limit. As such, inverter operation down to 6V in response to the battery supplied DC voltage dipping down is not feasible.